For the purpose of more adequately describing a technological level for the present invention at present, all descriptions of the patents, patent applications, patent gazettes, scientific papers, and the like which are cited or specified in the present application will be incorporated herein by reference.
Conventionally, an LSI test socket (hereinafter, referred to as an LSI socket) has been used to avoid thermal and mechanical damage to a solder ball in a BGA package when conducting a screening test on LSI incorporated in a high-density and multi-pin BGA package. An LSI socket used to accomplish this objective is largely divided into two types: a pogo-pin type and a sheet type.
The pogo-pin is called a spring pin or a spring probe pin, and composed of three components: a pogo-pin 001, a pin 002, and a spring 003, as shown in the cross-sectional view of FIG. 1. A pogo-pin type LSI socket using this pogo-pin is provided together with a pin in which coiled spring structure is supported by a resin casing to press above and below this pin, thereby providing the realization of an electrical connection.
FIG. 2A, FIG. 2B, FIG. 3A, and FIG. 3B are cross-sectional views showing the structure of conventional LSI sockets for BGA using pogo-pins, respectively. First, as shown in FIG. 2A and FIG. 2B, this LSI socket is composed of the pogo-pin 001 and a pogo-pin supporting casing portion 005 in combination. More specifically, the LSI socket has structure in which the pogo-pin 001 is inserted into a casing hole 010 from the upper side or the lower side of the pogo-pin supporting casing portion 005 which is made of nonconductive material such as resin.
FIG. 2A is a case in which the pogo-pin 001 is inserted into the casing hole 10 from the downside of the pogo-pin supporting casing portion 005 and fixed, with stoppers 006 located on the upper side of the pogo-pin supporting casing portion 005. On the other hand, FIG. 2B is a case in which the pogo-pin 001 is inserted into the casing hole 010 from the upper side of the pogo-pin supporting casing portion 005 and fixed, with the stoppers 006 located on the downside of the pogo-pin supporting casing portion 005.
In addition, FIG. 3A is a case in which the LSI socket with the structure of FIG. 2A is disposed on a test board 009, and FIG. 7B is a case in which the LSI socket with the structure of FIG. 2B is disposed on the test board 009. In either case, the pogo-pin 001 which is located corresponding to the position of a solder ball 007 of the LSI enclosed in the BGA package provides the realization of the electrical connection by pressing a wiring pad 008 on the test board 009 on which the LSI socket is mounted from above. In general, it is an advantage that this type of LSI socket is cheap in price because of simple structure, and may be repeatedly used because of great mechanical strength.
On the other hand, a sheet type LSI socket involves the use of a conductive sheet, and includes a metal fine wire embedded type and a conductive rubber type. The sheet type one may be shortened more than the aforementioned pogo-pin type one in pin length, and has the advantage of excellence in high frequency characteristics. However, the sheet type one has problems with much dust caused by metal oxide shavings, and high running cost due to expensive sheet, and further a problem with larger contact resistance because metal oxide is attached to the contacting surface.
Additionally, in the case of using any of these types of LSI sockets, a significantly serious problem has emerged along with high frequency and high power current operation of LSI in recent years. Test frequencies have become higher along with considerable performance improvement of LSI to be tested, and test conditions of the LSI incorporated in the BGA package have been conducted in a high frequency area of GHz order. This produces an extremely high power current, with the result that it is more likely that the potential fluctuation of power supplies and GNDs of the LSI occurs. There is another problem that it is difficult to supply power supplies with high quality in the vicinity of the BGA package because power supplies required for LSI operation are supplied from a tester far distant from the LSI when conducting an LSI screening test.
For this reason, if a capacitor cannot be disposed in the closest vicinity of a BGA package to be tested, a power current is produced by LSI high frequency operation to fluctuate the potential of power supplies and GNDs of the test board, leading to difficulty in ensuring operational stability of the LSI incorporated in the BGA package.
However, aside from this, a conventional LSI socket has an essential problem that a decoupling capacitor for reducing a swing of the potential fluctuation of the power supplies and the GNDs in the vicinity of the BGA package has become impossible to be mounted. It results from the facts that the number of electrodes of input/output signals, the power supplies and the GNDs of the LSI is increased by an improved integration degree more than before, and that the spacing between electrodes in the BGA package is narrowed to cause the electrodes to be densely packed by the miniaturization of the BGA package. In addition, even if the test frequency is less high, for example, LSI having as many as 512 of parallel input/output number has a problem that an enormously instantaneous power current flows at the time of 10 concurrent operation.
As a means of reducing the potential fluctuation of the power supplies and the GNDs described above, the sheet type LSI socket, for example, is intended to use a conductive sheet as a capacitor by connecting a plurality of electrodes on one side of the conductive sheet to a conductive layer, and allowing the conductive layer to be attached to the sheet to comprise a power supply layer, and by connecting a plurality of electrodes on the other side of the conductive sheet to the conductive layer, and allowing this conductive layer to be attached to the sheet to comprise a GND layer (for example, refer to Patent Document 1). This makes it possible to dispose a package sized capacitor immediately below the BGA package incorporating the LSI, whereby the effect of noise occurring in the power supplies and the GNDs at the time of the LSI high frequency operation may be reduced.
The conventional sheet type LSI socket described above has a problem with significantly difficulty in realization because of its structure, a problem with high running cost because of expensiveness and lack of sufficient stability for repeated use, and further a problem with lack of the contact ability of the LSI socket itself, with the result that it is not to be repeatedly used at a mass production level. Furthermore, the LSI in recent years mostly needs a plurality of power supply voltages, to which the sheet type cannot respond.
[Patent Document] Japanese Unexamined Patent Publication No. 2000-97991 (Page 3, FIG. 1 to FIG. 3)
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
Consequently, it is an object of the present invention to provide a pogo-pin type LSI socket containing a decoupling capacitor for reducing the potential fluctuation of power supplies and GNDs in the vicinity of a BGA package at the time of a test, although it is made to solve problems occurring when testing LSI enclosed in the BGA package with a very large number of pins of input/output signals, power supplies, and GNDs at high frequencies, easy to replace socket pins, and has pogo-pin structure with low cost and high stability.
[Means for Solving the Problem]
A first aspect of the gist of the present invention provides an LSI test socket for BGA which comprises a printed board containing at least one or more decoupling capacitors in which a first power plate connected to an inner surface of a first through hole and a second power plate connected to an inner surface of a second through hole are laminated through a separator, a pogo-pin supporting casing portion on which said printed board is overlapped into a single piece, and in which at least one or more pairs of first and second casing holes are each opened at positions corresponding to said first and second through holes, and at least one or more pairs of first and second pogo-pins inserted into penetrating holes in which hole positions of said first and second through holes drilled in said printed board, and said first and second casing holes are allowed to be matched, wherein one end of the printed board faces a BGA package, said pogo-pin supporting casing portion being disposed at the other end thereof at the time of testing LSI incorporated in the BGA package. It should be noted that a power plate is a plate spread like a sheet which supplies a power supply, but not a signal, and is made of foil and other material such as metal having the function of electrodes of the decoupling capacitor, as well as potential which is applied to this plate includes not only power supply voltage potential, but also medium, GND, and further negative potential.
Power supply layers each corresponding to said first and second power plates and one GND layer are formed in the printed board, and the decoupling capacitors may be formed by the use of an electrostatic capacity between the power supply layers and the GND layer.
In the printed board, plating layers may be formed in inner surfaces of through holes into which power supply pogo-pins and a GND pogo-pin are inserted, except for a through hole into which a signal pogo-pin is inserted.
The pogo-pin supporting casing portion is made of non-conductive material, and the plating layers need not be formed in inner surfaces of the casing holes.
And, the power supply layers may be electrically connected to the plating layers in the inner surfaces of the through holes into which the power supply pogo-pins are inserted, and said GND layer may be electrically connected to the plating layer in the inner surface of the through hole into which the GND pogo-pin is inserted.
A second aspect of the gist of the present invention provides an LSI test socket for BGA which comprises a printed board containing decoupling capacitors in which a first power plate connected to an inner surface of a first through hole and a second power plate connected to an inner surface of a second through hole are laminated through a separator, a pogo-pin supporting casing portion on which the printed board is overlapped into a single piece and in which first and second casing holes are each opened at positions corresponding to said first and second through holes, and pogo-pins inserted into penetrating holes in which hole positions of said first and second through holes drilled in said printed board, and said first and second casing holes are allowed to be matched, wherein one end of said pogo-pin supporting casing portion faces a BGA package, said printed board being disposed at the other end thereof at the time of testing LSI incorporated in the BGA package.
Power supply layers each corresponding to said first and second power plates and one GND layer are formed in the printed board, and the decoupling capacitors may be formed by the use of an electrostatic capacity between the power supply layers and the GND layer.
In the printed board, plating layers may be formed in inner surfaces of all through holes into which a signal pogo-pin, power supply pogo-pins and a GND pogo-pin are inserted.
Said pogo-pin supporting casing portion is made of non-conductive material, and the plating layers need not be formed in inner surfaces of the casing holes.
The power supply layer may be electrically connected to the plating layers in the inner surfaces of the through holes into which the power supply pogo-pins are inserted, and said GND layer may be electrically connected to the plating layer in the inner surface of the through hole into which the GND pogo-pin is inserted, while the plating layer in the inner surface of the through hole into which the signal pogo-pin is inserted need not be electrically connected to the power supply layers and the GND layer.
And, the pogo-pins may be fixed by inserting the bottom of the pogo-pins into each corresponding through hole of the printed board and soldering through the plating layers.
[Effects of the Invention]
In accordance with the present invention, the potential fluctuation of power supplies of LSI operating at high frequencies may be reduced to allow for a stable operation test by containing a decoupling capacitor in an LSI socket for BGA. In addition, an LSI socket for BGA having better manufacturing stability and test stability may be realized by that a self-contained portion of the decoupling capacitor and a pogo-pin supporting casing portion are separated into portions of another layers.